Chemistry 251/253

Answer Key

Homework 12
1. How many isomeric ketopentoses are there? 7

2.* Draw the structure of a ketopentose that is optically inactive. Refer to the JavaGrins tutorial for instructions on how to draw Fischer projections of sugars.OC[C@H](O)C(=O)[C@H](O)CO or OC[C@@H](O)C(=O)[C@@H](O)CO

3. Enter the number of the anomeric carbon in .6

4.is

A. an aldopentose
B. a ketopentose
C. an aldohexose
D. a ketohexose
E. none of these

5. Select the cyclic form of Compound c.

6. What is the IUPAC name of

a. 2R,3R,4-trihydroxybutanal
b. 2R,3S,4-trihydroxybutanal
c. 2S,3R,4-trihydroxybutanal
d. 2S,3S,4-trihydroxybutanal

7. b

8. Select the monosaccharide that yields when subjected to Ruff degradation.

a. D-(-)-erythrose
b. D-(-)-ribose
c. D-(+)-allose
d. D-(-)-xylose

9. Select the structure that you would use as a model compound for the investigation of mutarotation. c Mutarotation requires a hemiacetal or hemiketal unit.

10. How many of the following compounds would undergo mutarotation when dissolved in water? 1 The 3rd structure contains a hemiacetal unit.

11. Consider the equilibrium between compounds F and P:. The specific rotation of compound F is -132 degrees. This decreases to -92 degrees at equilibrium. What is the specific rotation of P? Enter your answer to the nearest integer.

12. Vitamin C, , is produced from D-glucose in many plants and animals. How many stereoisomers of vitamin C are there? 4 You can't form a 5-membered ring in which the two OH groups attached to the double bond are trans to each other.

13. Draw the structure of the product of the following reaction: CC1(C)OCC(O1)C=O

14. Select the compound that would give the same osazone as .a

Consider the following scheme, in which compound A is a D-aldohexose other than D-glucose. Then answer questions 15-17.

15. Enter the name of a D-aldohexose other than glucose that the results of oxidation of compound A with nitric acid eliminates as a possible structure for compound A. Do not include the designation D. allose and galactose are not consistent with this data.

16. How many structures are eliminated by the results of Ruff degradation of A followed by oxidation of the resulting aldopentose? 3- altrose, gulose and idose are not consistent with this information.

17. What is the name of compound A. Do not include the designation D.talose

18.Which of the following designations most accurately describes the outcome of the reaction?

a. (R)-(+)
b. (R)-(-)
c. (S)-(-)
d. (S)-(+)
e. (S)

19. Select the conformation of 1-chloro-2-methylcyclohexane from which the following dehydrochlorination occurs:b This is an E2 reaction. The dihedral angle between the C-H bond and the C-Cl bond has to be 180 degrees.

20.Treatment of C6H4Cl2 with Br2/Fe produced two compounds with the formula C6H3BrCl2. Draw the structure of the isomer of C6H4Cl2 that is consistent with this data. 1,2-dichlorobenzene Clc1ccccc1Cl

21.Draw the structure of the compound that gives the 1H and 13C-NMR spectra shown below.CC(C)(C)C=O

22.Consider the Friedel-Crafts methylation of toluene. When the reaction is run at 0oC, the p-xylene is formed in the highest percentage and m-xylene the lowest. At 80oC the major product is m-xylene. Select the reaction profile that is most consistent with this information.d The first piece of information tells you that p-xylene has the lowest activation energy. The second piece indicates that m-xylene is the most stable of the three isomers

23.Select the compound that would not be formed in the following crossed aldol condensation:

 

e

24.If you had an aqueous solution of the same concentration of each of the following compounds, which one would have the lowest conductance?

a. ClCH2CO2H
b. CF3CO2H
c. CH3CO2H
d. C6H5OH
e. CF3CH2OH

25. Enter the letter(s) of any ion(s) that can't exist in aqueous solution at any appreciable concentration.

a. -:I
b. CH3CO2:-
c. -:NH2
d. -:CH3
In order to have a significant concentration of an ion present in aqueous solution, that ion can't be more basic than hydroxide ion. If it is more basic, then it will react with water to produce hydroxide ion. In other words, if the pKa of the conjugate acid of a salt is much greater than the pKa of water, then the salt will react with the water. For example, adding sodium amide, NaNH2 to water results in the following reaction:. Keq for the reaction of water with -CH3 is even larger, 1034.

26. Arrange the following compounds in order of increasing acidity: b<c<a

27. Select the major product that should be formed in the reaction sequenceb

28. The following reaction produces a mixture of products. Draw the structure of the product for which the 1H-NMR spectrum is provided.CCCCC(CBr)OC

29. Draw the structure of the lowest molecular weight hydrocarbon that contains enantiotopic hydrogens.CCC#C

30.A compound with the molecular formula C6H10O2 contained two carbons in the -3 oxidation level, one carbon in the -2 oxidation level, one carbon in the -1 oxidation level, one carbon in the 0 oxidation level, and one carbon in the +3 oxidation level. Draw the structure of this compound.CCOC(=O)C(=C)C

There were multiple correct answers to this question. I have given each of you one more point than appears in your grade report for this assignment. Even though the report may indicate you answered question 30 incorrectly, you have received credit for this problem.